Modulation indicator



Oct. l, 1940.

L. B. HOLMES MODULATION INDICATOR Filed May 24, 1938 2 Sheets-Sheet l In 'INAH L; B. HOLMES MoDuLATIoN INDICATOR Filed May 24, 1938 2 Sheets-Sheet 2 SKY INVENTOR.

Oct. 1, 1940.

Patented Oct. l, 1940 UNITED STATES PATENT orifice` 4 Claims.

generally. More particularly this invention relates to a method and apparatus Ior indicating modulation in apparatus such as radio telephone tent to which the tube is energized.

Another object of this invention is to provide a modulation indicator for radio telephone transmitters, said modulation indicator employing a tube with a fluorescent screen which is` adapted to act modulation indicator.

A further object of this invention is to provide an electrically energized indicating tube of elongated shape 'in which dii'erent sections ot the tube are coated with different types of uorescent materials to produce different color indications, said fluorescent materials being so arranged that the tube when energized by a speech or otherwise modulated or varied electric current will give different indications depending upon the intensity, loudness or volume of the speech or other modulating or varying energy.

' Another object is to provide an electrical indicator comprising a tube with a plurality of screens of iiuorescent material, different ones of said screens being excited and caused to become luminescent when different sound energy or other energy levels are to be indicated.

Still another of this invention is to provide a modulation indicator employing a tube made o!r relates claims.

from the following specification and the In accordance 'with this invention I provide a simple and efiicient indicator which may be made relatively accurate and without great expense.

One of the uses of the indicator of my invention is to indicate when the radio signal emitted by a radio telephone transmitter is modulated over However, it will be obvious that this in# (Cl. 1ML-171.5)

This invention relates to electrical indicators dicator may be calibrated to indicate various percentages of modulation and of course my invention is not to be limited to an indicator adapted for the 100% indication only. My indicator consists primarily of an elongated glass 5 tube which is provided with an electrode at one end connected by means of a small condenser to one of the high frequency circuitsoi the radio transmitter. The inside of this glass tube is coated with iiuorescent materials by sucking solul0 tions containing such materials up into the tube to the desiredheight. When the solutions are emptied from the tube by cutting of! the suctionl a coatingof the desired material remains on the inside wall of the tube. The air is exhausted i'rom the tube and inert gas or a mixture of inert gases placed therein to facilitate electrical bombardment of the iluorescent screen through ionization oi.' the inert gases. This ionization does not have to be visible and the pressure of the inert gases in the tube should be relatively low when compared to atmospheric pressures. A small quantity of mercury may be placed inside of the tube to produce a brighter iluorescence of the screen material of the tube. The ultra violet rays produced through the action of the mercury vapor in the tube also excite the screen and assist the bombarding action in causing the screen to become fluorescent.V The top of the tube, that is the end opposite the end provided with the electrode, is provided with a small cap which is connected to the metal chassis of the radio transmitter of low power. This connection may not be necessary where the indicator is used with transmitters of relatively high power.

After the indicator is connected to the transmitter as outlined above the small coupling condenser is adjusted so that the tube indicates at the no-modulation point. This is when the transmitter is not being modulated and only the u un-modulated carrier wave is being transmitted. When this adjustment for no-modulation is obtained the indicator is set to indicate when the Asignal of the transmitter is modulated over 70 of one type of luminescent material, for example.

vention. Among these various uses is that of indicating the sound intensity of a person speaking or singing into the microphone of a radio broadcasting station. public address system` or any telephone circuit. The indicator tube of my invention is easily applied to this use simply by connecting suitable electrodes in the tube to thev output circuit of an ampliner so that some of the voice modulated currents developed in the microphone are amplified and impressed upon the indicator tube. s

Further details of this invention may be obtained from the following specification and the drawings in which, briefly, Fig. 1 illustrates the indicator of my invention and a diagram of connections employed therewith; Fig. 2 is a cross section of the tube taken along the lines of 2-2 of Fig. 1; Fig. 3 is a cross section of the tube taken along the lines of 3 3 ofvFig. 1; Fig. 4 illustrates another embodiment of this invention and Fig. 5 is a schematic diagram showing still another arrangement of this invention.

Referring to the drawings more particularly,

reference numeral I0 designates an elongated tube made of transparent material, s uch as glass, Bakelite fused quartz, Pyrex and the like. An electrode I I made of material, such as, nickel, tungsten. graphite, or the like, is supported by the wire I2 which is fused into one end of the tube and projects through the glass material to contact the cap I3 of brass or similar material positioned on the outside of the glass tube. This contact I3 is connected at Il to the wire I5 and the variable condenser` I6. 'I'he other end of the tube I0 is provided with a cap I'I of metallic material. This cap I'I is not connected to the inside of the glass tube by any metallic connection. However when the potential is applied to this cap with respect to the electrode II an electrostatic field is set up between this cap and the aforesaid electrode which is desirable in the operation of the device.

'I'he condenser I 6 is connected by the wire 22 and a variable top 22a to the tank coil 23 of the high frequency power amplifier tube 2l of the radio transmitter 25. This power amplifier 2l amplifles the high frequency oscillations fed to it by the oscillator-buffer apparatus 28 and is modulated by the modulated tube 21 to which is connected the microphone 28. 'Ihis circuit ar.

rangement, that is, the circuit of the radio transmitter is conventional and well known in the art and is illustrated here only for the purpose oi' showing an application of my modulation indicator and the method of operation thereof. The transmitter in this case is housed in the metal cabinet 29 to which the cap I'I isconnected by the wire 30.

The inside of the tube III is coated with particles forming the screens I8 and I9 of fluorescent material. Various substances, such as, willemite (zinc orthosilicate). zinc sulfide, zinc-cadmium sulfide, zinc silicate, calcium tungstate, and the like or combinations thereof may be employed as the luminescent screen material. These materials possess the property of fluorescence when they are subjected to electric bombardment and phosphorescence immediately thereafter. In the present invention I employ a screen I8 made up willemite or the like.' This screen I0 is substantially continuous along the inner walls of the glass tube III from the adjacent electrode II to the line 20 marked on the outside the glass tube.

The line 2l is designated as the 100% modulation point. Adjacent to the electrode II may be'provided a' line 2| which is designated as the "no modulation point. 'I'he screen I3 extends from the line 2t to the end of the tube underneath the cap I 1 and ,this screen is made up a.,

different luminescent material from thatA out oi' which the screen` I8 is made. The PllrDOle for this is to obtain a clear indication when modulation in excess of 100% is produced in the signal of the radio transmitter. For example when modulation up to 100% is produced only the screen Il will be excited and caused to become luminescent by electric bombardment. When, however modulation in excess of 100% is affected-in the radio signal portions of the screen Il will be excited. In order to produce a better indication of excessive modulation it may be desirable to make the screen I9 of material which is phosphorescent aswell as uorescent so that it remains luminescent for a period after excitation thereof. In this way the modulation peaksare more clearly indicated.

The tube I0 is thus calibrated so that the line 20 indicates the 100% modulation point and the line 2l indicates the no modulation point.v Once the tube is thus calibrated the indications obtained therefrom may be duplicated and the operation of the tube is reliable and uniform.` In order to insure this a small globule of mercury 3| is placed lntothe tube. The amount of mercury should preferably be very small although the quantity used is not critical.

In operation the tube is connected to the tank coil 23 of the transmitter through an adjustable connection or clip 22a and the variable condenser is adjusted so that the screen Il will become uorescent up to the line 2| when the transmitting set is not being modulated. In the circuit diagram I have illustrated thev connection 22a close to the high potential end of. the inductance 23 and it is of course obvious that this connection may be moved toward the lower potential end of this inductance if the indication in the tube can not be brought down to the line 2| by adjusting the condenser I6. 'Ihe antenna coupling coil which is shown coupled to the lower end of the inductance 23 also may be shifted towards the high potential end if desired. However the adjustments o f the antenna coilv and the other circuits of the transmitter are well known in the art ofradio transmission and will not be discussed in detail in this specification except insofar as they relate to this invention.

Where desired the tube I0 and condenser Il with the associated connections may be built into the radio transmitter and a suitable slot cut into the front panel of the transmitter lto enable the operator to view the tube III from the front of said panel. In .this case only the portion between the lines 20 and 2I and a small section above and below these lines need be visible through the aforesaid slot so that the indicator may be adjusted to indicate no modulation operation of the transmitter and 100% or more modulation. l

In cases where the tube I0 is not mounted inside the transmitter it is desirableto hide the electrode II from view and this is accomplished Vby placing a coating of non-conductive paint,

iii)

plifiers are illustrated in Figs. 4 and 5. The tubes illustrated in these figures each employ an elongated electrode llc extending substantially throughout the length of the tube. Auxiliary electrodes Ila and i lb are also employed inthe tube shown in Fig. 4 and in this Acase the electrode IIb is connected to the positive terminal of the amplifier anode current supply. The electrode Ila is connected to the metal chassis or frame of the amplifier and to a terminal of the secondary 35 of the output transformer 36 connected to the amplifier. The other terminal of the secondary 35 is connected to the electrode ilc. In this form of the tube I0 an electric discharge is normally maintained between the electrodes lia and I Ib inasmuch as the electrode lib is connected to the positive terminal of the power supply and the electrode Ila is connected to the amplifier chassis which is usually connected to a negative terminal oi' the same power supply. The secondary 35 impresses an alternating potential across the electrodes ila and lic. This aiternating potential corresponds to the speech, music or other frequencies impressed upon the input of the amplifier to which the transformer it is connected. In cases where the amplifier characteristics are such as to amplify the speech, rnusic or other frequencies logarithmically the tube ill, excited from the output of such an amplifier, must be made extremely long'. However the necessity for making this tube of unusual length may be eliminated by adjusting the characteristics of the amplifier so that the voltage amplification thereof bears a linear relation to the amplitude of the speech, music or other freauencies impressed on the input of the amplifier.

The tube IU shown in Figs. 4 and 5 is provided with three fluorescent screen sections I8, i9 and ita and each of these screen sections is made up of different fluorescent material so that different sound amplitudes impressed upon the input of the amplifier may be more readily indicated. Sounds of low amplitude are indicated by fluorescence of the screen I8; sounds of intermediate amplitude are indicated by the fluorescence of the screen i9 and likewise sounds of higher amplitude are indicated by the fluorescence oi' the screen iSa. It is of course obvious that any amplitude calibration desired may be placed on these screens and more than three screens of distinct characteristics may be employed.

The form of the tube l0 shown in Fig. 5 also employs the elongated electrode ilc which is connected to the secondary 35 of the output transformer 36. The windings 35 and 31 of this transformer are connected together and this common connection is connected to the positive terminal of the amplifier power supply so that the primary :il is between the power supply and the anode of an amplifier tube and the secondary iii is connected between the tube i0 and the power supply. The auxiliary electrode ila in this case is connected to the chassis of the amplifier. .an electric discharge is maintained between this electrode and the bottom portion of the electrode llc inasmuch as a direct current potential, supplied by the amplifier power supply, is impressed across these two electrodes. When an alternating potential which may correspond to the speech, music or other frequencies is im pressed across the electrodes I la and I Ic through the operation of the transformer secondary 35, different portions of the screens i8, I9, Isa which are adjacent to the electrode Hc, will be energized and become luminescent depending upon Vstation microphone.

the amplitude of the potential impressed on the tube from the secondary 35.

This form of the tube i0 has numerousI applications, one of the principal uses in the nature of a monitor for speakers 'or singers speaking or singing into a radio broadcasting By observing the fluorescence of the various screens of the tube il) the speaker or singer will know at all times whether or not he is speaking or singing too loud into the microphone and may move to or away from the microphone so as to deliver the properv sound intensities thereto.

It is obvious that the indicator of my invention may be made in different forms without departing from the spirit or scope of this invention and therefore I do not desire to limit this device to the exact details described and illustrated except insofar as those details may be defined by the claims.

I claim:

i. indicating apparatus for indicating the amplitude of modulations of electrical oscillations particularly when said amplitude may be excessive, comprising: an elongated tube having substantially greater length than breadth, electrode means positioned in one end of said tube, means for impressing electrical oscillations on said electrodes for producing the desired indications, a screen of fluorescent material covering substantially the entire length of the inner wall of said tube so as to be seen from the outside thereof, different sections of said screen being of uorescent material having different color characteristics when energized, a rarifled atmosphere and material in said tube to excite ultra violet light therein to energize the different sections of said screen depending upon the amplitude of the modulated electrical oscillations impressed upon said electrode means..

2. indicating apparatus for indicating the amplitude of modulations of electrical oscillations particularly when said amplitude may be excessive, comprising: a modulated radio transmitter having a tank circuit, an elongated tube having substantially greater length than breadth, electrode means positioned in one end of said tube, connections to said tank circuit including a variable condenser for impressing electrical oscillations on said electrodes from said modulated transmitter for producing the desired indications, a screen of fluorescent material covering substantially the entire length of the inner wall of said tube so as to be seen from the outside thereof, different sections of said screen being of fluorescent material having different color characteristics when energized so that the amplitude of the modulations may be determined by observing the sections of said tube. a raried atmosphere and material in said tube to excite ultra violet light therein to energize the different sections of said screen depending upon the amplitude of the modulated electrical oscillations impressed upon said electrode means.

3. Indicating apparatus for indicating the amplitude of modulations of electrical oscillations particularly when said amplitude may be excessive, comprising: an amplifier, an elongated tially the entire length of the inner wall of said tube so as to be seen from the outside thereof, diil'erent sections of said screen being of fiuorescent material having different color characteristics when energized so that the amplitude of the modulations may be determined by observing the sections of said tube, a raried atmosphere and material in said tube to excite ultra violet light therein to energize the different sections oi.' said screen depending upon the amplitude of the modulated electrical oscillations impressed upon said electrode means.

4. Indicating apparatus for indicating the amplitude of modulations of electrical oscillations particularly when said amplitude may be excessive, comprising: an ampliiler, an elongated tube having substantially greater length than breadth, a plurality of electrodes positioned in one end of said tube, one of saic electrodes being elongated and substantially co-extensive with the interior of said tube, connections for impressing a relatively high potential on said elongated electrode from said amplier output with respect to the other of said electrodes for producing the desired indications, a screen of fluorescent material covering substantially the entire length of the inner wall of said tube so as to be seen from the outside thereof, different sections of said screen being of iluorescent material having different color characteristics when energized, a raried atmosphere and material in said tube to excite ultra violet light therein to energize the different sections of said screen depending upon the amplitude of the modulated electrical oscillations impressed upon said electrode means.

LESTER B. HOLMES. 

